Apparatus and method for channel access

ABSTRACT

A channel access method and apparatus are disclosed. The channel access method by an access point (AP) having a sector antenna in a wireless local access network (WLAN), may include transmitting a sector beacon with respect to any one sector among a plurality of sectors, transmitting and receiving data with at least one station in any one sector during a pre-scheduled sector interval, sequentially performing transmission of the sector beacon and transmission and reception of the data with respect to remaining sectors of the plurality of sectors excluding the any one sector, transmitting an omni beacon with respect to all of the plurality of sectors, and transmitting and receiving data with respect to at least one station of the plurality of sectors during a pre-scheduled Basic Service Set (BSS) interval.

TECHNICAL FIELD

The present invention relates to a channel accessing apparatus andmethod in a wireless local access network (WLAN) system.

BACKGROUND ART

FIG. 1 is a diagram showing a hidden node problem occurring in aconventional WLAN system.

In the WLAN system, when a plurality of stations STA 111 and 112 in asame Basic Service Set (BSS) perform data transmission with respect toan access point (AP) 100 simultaneously, air-time collision inevitablyoccurs due to characteristics of a channel access scheme in view ofcollision avoidance, which is a hidden node problem.

In addition, even when stations located in different adjacent BSSsperform data transmission, an interference may also be generated asshown in FIG. 2, thereby reducing efficiency of data transmissionoriginally desired. This is referred to as an overlapped BSS (OBSS)interference problem. FIG. 2 shows the OBSS interference problemoccurring in the conventional WLAN system.

To relieve such problems, access chances of stations may be temporallydistributed in every BSS to avoid collision on frequency resources.However, the foregoing expected object may also be achieved by spatiallydistributing channel access attempts using an AP with a sector antenna.Such a technology is called sectorization.

In general, the sector antenna includes a plurality of planar antennasand may control flickering of individual transmission antennas andreception antennas. A device functioning as the sector antenna may beimplemented using a combination of multiple antennas and signalprocessing such as beam forming. The sectorization has not been used inthe conventional WLAN nor even technically discussed, due to itsoperational inconvenience.

However, in case of institute of electrical and electronics engineers(IEEE) 802.11ah and IEEE 802.11af that use a sensor application,indoor/outdoor M2M, and extended range cellular offloading as a mainapplication, coverage is increased up to about 1 km. Furthermore, as anumber of stations managed by one BSS is increased up to severalthousands to several tens of thousands, the hidden node problem and theOBSS interference problem become so serious that efficient datatransmission cannot be performed at all. Accordingly, there is a demandfor a technology of considerably reducing the problems by spatiallydividing operation of stations through sectorization in the WLAN system.

DISCLOSURE OF INVENTION Technical Solutions

According to an aspect of the present invention, there is provided achannel access method by an access point (AP) having a sector antenna ina wireless local access network (WLAN), the channel access methodincluding transmitting a sector beacon with respect to any one sectoramong a plurality of sectors, transmitting and receiving data with atleast one station in any one sector during a pre-scheduled sectorinterval, sequentially performing transmission of the sector beacon andtransmission and reception of the data with respect to remaining sectorsof the plurality of sectors excluding the any one sector, transmittingan omni beacon with respect to all of the plurality of sectors, andtransmitting and receiving data with respect to at least one station ofthe plurality of sectors during a pre-scheduled Basic Service Set (BSS)interval.

The channel access method may further include performing a sectordiscovery process by performing sector sweep.

Effects of Invention

By applying sectorization in a wireless local area network (WLAN)system, a Basic Service Set (BSS) operation robust against a hidden nodeproblem and an overlapped BSS (OBSS) interference problem may beachieved. In addition, the sectorization may be useful in electrical andelectronics engineers (IEEE) 802.11ah and IEEE 802.11af that use a WLANsensor application.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a hidden node problem occurring in aconventional wireless local area network (WLAN) system.

FIG. 2 is a diagram illustrating an overlapped Basic Service Set (OBSS)interference problem occurring in a conventional WLAN system.

FIG. 3 is a diagram illustrating a spatial configuration of a BSS when anumber of sectors is 3 in a WLAN system according to an embodiment ofthe present invention.

FIG. 4 is a flowchart illustrating a channel access method by an accesspoint (AP) having a sector antenna in a WLAN system according to anembodiment of the present invention.

FIG. 5 is a diagram illustrating a beacon and an interval in asectorized case, according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating a temporal configuration of a sectorsweep according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating an operation in which a channel accessoccurs in a sector interval.

FIGS. 8 and 9 are diagrams illustrating a beacon message and an intervalin a WLAN system according to another embodiment of the presentinvention.

FIG. 10 is a diagram illustrating sectorized beam operation according toan embodiment of the present invention.

FIG. 11 is a diagram illustrating a beacon message according to yetanother embodiment of the present invention.

FIG. 12 is a diagram illustrating a sector training operation in asectorization type 0, according to an embodiment of the presentinvention.

FIG. 13 is a diagram illustrating a sounding restricted access window(RAW) and a sector report RAW according to an embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings.

In explaining the embodiments of the present invention, generally knownfunctions and structures will not be explained in detail not to obscurethe scope of the invention. In addition, terms to be used below aredefined to properly explain exemplary embodiments of the presentinvention and may vary according to users, user's intentions, orpractices. Therefore, the definitions of the terms should be determinedbased on the entire specification. In the drawings, like referencenumerals refer to the like elements throughout.

A channel access method according to an embodiment of the presentinvention refers to a channel access method of a Basic Service Set (BSS)including an access point (AP) including a sector antenna in a wirelesslocal area network (WLAN) system.

FIG. 3 is a diagram illustrating a spatial configuration of a BSS when anumber of sectors is 3 in a WLAN system according to an embodiment ofthe present invention.

In the environment as in FIG. 3, the channel access method maytemporally divide flickering time of sector antennas of an AP. Each ofthe sector antennas may be in charge of transmission and reception ofstations located in each direction. That is, the AP may distinguishflickering times of a first sector 311, a second sector 312, and a thirdantenna 313.

FIG. 4 is a flowchart illustrating a channel access method by an APhaving a sector antenna in a WLAN system according to an embodiment ofthe present invention.

In operation 410, the channel access method may transmit a sector beaconwith respect to any one sector among a plurality of sectors.

In operation 420, the channel access method may transmit and receivedata with respect to at least one station in any one sector thattransmitted the sector beacon during a predetermined sector interval.That is, according to the channel access method, data transmission andreception of stations in each sector may be performed within a sectorinterval with respect to a sector of which a corresponding station ismapped.

After the sector interval is elapsed, in operation 430, the channelaccess method may sequentially perform transmission of the sector beaconwith respect to remaining sectors among the plurality of sectors(operation 410) and transmission and reception of data (operation 420).This will be described again with reference to FIG. 5.

After the sector beacon transmission and the data transmission andreception are completed with respect to all sectors, the channel accessmethod may transmit an omni beacon with respect to the all sectors inoperation 440 because the omni beacons are necessary to be equallytransmitted to the all sectors even in case of sectorization, forassociation, passive scanning, broadcasting, and multi-sectortransmission.

In operation 450, the channel access method may transmit and receivedata with respect to at least one station in the plurality of sectorsduring a predetermined BSS interval. Depending on embodiments, as to atraffic indication map (TIM), the channel access method may notify a TIMwith respect to a sector-dedicated station in the sector beacon, and theother matters in the omni beacons.

With respect to other transmission and reception such assector-dedicated transmission and reception, broadcasting, multi-usermultiple input multiple output (MU-MIMO) across sectors, and the like,the channel access method may temporally distinguish by sector intervalsand BSS intervals.

Depending on embodiments, the channel access method may return partialtime periods even in the sector interval for transmission and receptionof other sectors or multi-sectors.

In case of a non-TIM device that allows staying in a sleep mode withoutlistening to the beacon, since the non-TIM device is unaware of itssector number, the channel access method may allow omni-directionaltransmission and reception and also allow to awake the BSS intervals inwhich temporal periods are fixed.

The channel access method may map the sector beacon and the omni beaconwith relationships between a short beacon and a full beacon inconsideration of frequency of the sector beacon and the omni beacon.FIG. 5 shows an example of the foregoing process.

FIG. 5 is a diagram showing a beacon and an interval in a sectorizedcase, according to an embodiment of the present invention.

Referring to FIG. 5, when the number of sectors is three, the channelaccess method may transmit a sector beacon 510 with respect to a firstsector. During a predetermined first sector interval 511, the channelaccess method may transmit and receive data with respect to at least onestation of a first sector.

After the first sector interval 511 is elapsed, the channel accessmethod may transmit a sector beacon 520 with respect to a second sector.During a predetermined second sector interval 521, the channel accessmethod may transmit and receive data with respect to at least onestation of a second sector.

In the same manner, after the second sector interval 521 is elapsed, thechannel access method may transmit a sector beacon 530 with respect to athird sector. During a predetermined third sector interval 531, thechannel access method may transmit and receive data with respect to atleast one station of a third sector.

After the third sector interval 531 is elapsed, the channel accessmethod may transmit an omni beacon with respect to all sectors, that is,the first sector, the second sector, and the third sector.

Depending on embodiments, the channel access method may transmit theomni beacon by broadcasting irrespective of the sectors. In addition,the channel access method may record information on TIM with respect toall remaining cases except for a particular sector-dedicated case andwindow time per group. Here, the RAW for the sector-sweep, themulti-sector MU-MIMO transmission, and broadcast transmission may beincluded. The sector-sweep will be described in detail later.

The channel access method may also record time information related toreturn or re-return of time periods to other sectors in each sectorinterval. Depending on embodiments, the channel access method mayinclude contents of the sector beacon again in the omni beacon.

According to an aspect of the present invention, a receiving mode of asector antenna of an AP may be omni-directional.

When a station is to perform association without listening to thebeacon, the station may try active scanning Here, since the AP is yetunaware of a region including the station trying the active scanning,the receiving mode of the sector antenna may be set to theomni-directional mode so that the AP successfully receives a proberequest. That is, the antenna of the AP may be set to perform sectortransmission only when performing downlink transmission. Depending onembodiments, since the probe request is received omni-directionally anda probe response may be transmitted also omni-directionally, the channelaccess method may use an exchange sequence informing of location of thesector, by referencing a sweeping omni beacon later.

Depending on embodiments, the channel access method may use a sectorcapabilities information element (I.E.) including a sectorized beamcapable field, a sectorization type field, a total sector number field,and the like, for sector capabilities exchange. A table below shows thesector capabilities I.E.

TABLE 1 Sectorized Total Elements beam Sectorization sector Re- IDLength capable type number served 8 8 1 2 4 1

In the channel access method according to the embodiment of the presentinvention, when dot11S1GSectorImplemented is true, the station may set avalue 1 for the sectorized beam capable field of the sector capabilitieselement in an association request frame. The station may also set avalue for the sectorized type field according to whether thesectorization operation is a type 0 or a type 1, in the sectorizedcapabilities element. The sectorization operation type will be describedagain later. When dot11S1GSectorImplemented is false, the station mayset a value 0 for the sectorized beam capable field of in the sectorizedcapabilities element.

When dot11S1GSectorImplemented is true, the AP may set a value 1 for thesectorized beam capable field of the sector capabilities element in theassociation request frame. The AP may set a value for the sectorizedtype field according to whether the sectorization operation is a type 0or a type 1, in the sectorized capabilities element, and set a value forthe sectorized type field to indicate a total number of the set sectors.When dot11S1GSectorImplemented is false, the AP may set a value 0 forthe sectorized beam capable field in the sector capabilities element.

In addition, according to the channel access method according to theembodiment of the present invention, a sectorized beam-capable APcapable of transmitting a sectorized beam may allocate or reallocate aparticular sector identifier (ID) to a sectorized beam-capable station(STA) capable of receiving the sectorized beam after the association. Asectorized beam-capable STA capable of transmitting the sectorized beammay selectively transmit a sector ID feedback to the sectorizedbeam-capable AP capable of receiving the associated sectorized beam. Thesectorized beam-capable STA capable of transmitting the sectorized beammay selectively request sector training of the sectorized beam-capableAP capable of receiving the associated sectorized beam.

The channel access method may further perform a sector discovery processby performing the sector sweep.

This is because the stations are unaware of corresponding sectors thestations belong to during the association and therefore additionallyneed the sector discovery process to discover the corresponding sectors.Here, the association may be performed through the omni-beacon. Thesector sweep may be performed using a temporally fixed or variedlocation.

Hereinafter, the sector discovery process will be described in detail.

In case of the sectorization, the stations need to find thecorresponding sectors and also need to share the information, that is,the corresponding sectors, with the AP so that the AP may provide thecorresponding sector interval period with transmission and receptionchances with respect to the stations.

In addition, the channel access method may perform the sector sweep forlistening of several sectors without temporal overlap so as to performthe sector discovery process stably and reliably.

Depending on embodiments, the channel access method may define thesector sweep as a signal sequence of a no data protocol (NDP) type.Therefore, the channel access method may reduce time duration. The NDPtype sector sweep may be illustrated as shown in FIG. 6.

FIG. 6 is a diagram illustrating a temporal configuration of a sectorsweep according to an embodiment of the present invention.

Referring to FIG. 6, an NDP sector sweep signal may include STF-LTF1-SIGwithout data. The NDP signal of each sector may include at least onepiece of information selected from a total number of sectors, a currentsector number of this NDP, an AP address, and the like.

Depending on embodiments, the channel access method may use a 1 MHz or 2MHz preamble format in case of 1 MHz or 2 MHz BSS of 802.11ah. In caseof 4/8/16 MHz BSS, the channel access method may use a signal (SIG) withrespect to a previous channel or a frequency duplicate type SIG of 1 MHzor 2 MHz.

Signals of each sector NDP may include at least one piece of informationselected from the total number of sectors, the NDP, the AP address, andthe like.

A following table shows a configuration of a SIG bit field of the NDPsector sweep in the 1 MHz BSS of 802.11ah.

TABLE 2 Field Bit width Comments Message type indicator 4 Unused MCSfield in normal data packet TA 9 (partial) BSSID Total number of sectors4 (or less) Current sector number 4 0~15 Reserved 5 Tail bits 6 TBD(Depending on group's decision on tail bit support) CRC 4 TOTAL 36 2 MHzcase, there are 12 reserved bits

Depending on embodiments, the channel access method may designate thesector sweep as a restricted access window (RAW). Since the sector sweepis designated as the RAW, reduction in the sector discovery efficiencyby transmission and reception of another random sector or sectors may beprevented. Also, reduction in transmission and reception efficiencycaused by the sector discovery may be prevented. The channel accessmethod may not allow transmission and reception of other purposes duringa corresponding time period since the sector sweep is designated as theRAW.

The channel access method may perform the sector sweep in a BSSinterval. That is, the NDP sector sweep protected by the RAW may beindispensably arranged in the BSS interval by scheduling information peraccess group provided by the omni beacon.

Depending on embodiments, in a passive scanning device, theindispensable RAW of the NDP sector sweep may be arranged right afterthe omni beacon or after a short inter frame spacing (SIFS) time, sothat the channel access method may enter the association being aware ofthe sector in advance after listening to the omni beacon.

Here, the omni beacon may include a location of the sector sweep in apre-m scheduled BSS interval. That is, the location of the NDP sectorsweep RAW may be pre-scheduled in the BSS interval or notified inadvance by the omni beacon.

Depending on embodiments, the channel access method may arrange the NDPsector sweep RAW not only in the BSS interval but also in a time periodexceptionally allowed for multi sector transmission and reception sothat the sector discovery process may be quickly performed withouthaving to wait until the BSS interval. Thus, even when the NDP sectorsweep RAW is arranged in the sector interval, the channel access methodmay pre-schedule the location of the NDP sector sweep RAW and notify thelocation through the omni beacon.

The station may discover its optimal sector through the sector discoveryprocess. When the optimal sector is found, the station may report theresult to the AP. Here, the station may report through an associationrequest or through a dedicated frame requesting associationidentification (AID) reassignment.

Through the sector discovery process, the channel access method mayreceive the result of discovering the optimal sector of the station fromthe station. Depending on embodiments, the channel access method mayfurther perform confirmation of the AP through transmission of thecorresponding sector with respect to a corresponding sector number ofthe station.

Each station may discover its optimal sector by receiving a mandatorysector sweep RAW located in the BSS interval or receiving apredetermined additional sector sweep RAW located in an exceptionalperiod in the sector interval. However, the station may request thesector discovery even with respect to a period in which the sector sweepRAW is not notified in advance by the omni beacon. In addition, based onthe sector discovery request, the station may transmit the additionalsector sweep RAW according to determination by the AP.

Thus, the channel access method may perform a fast sector discoveryprocess. In detail, the channel access method may receive a sectordiscovery request from a station to perform the fast sector discoverywith. Also, the channel access method may perform the additional sectorsweep besides the predetermined sector sweep. In addition, the channelaccess method may receive a result of the fast sector discovery processfrom the station.

Even with respect to the period in which the sector sweep RAW is notpre-scheduled, the channel access method may additionally have anexceptional sector sweep RAW during a time period returned to othersectors of the sector interval, based on the fast sector discoveryrequest transmitted from the station, that is, through the determinationby the AP. According to such a process, when the station transmits thesector discovery request, which may include an AP address, to the AP andwhen the AP transmits the additional sector sweep through thedetermination based on the request received from several stations, thecorresponding stations may report the found sector. During the fastsector discovery request, the station may also transmit urgency ofdiscovery to the AP.

FIG. 7 is a diagram illustrating an operation in which a channel accessoccurs in a sector interval.

As described above, data transmission and reception of each station maybe performed only within a sector interval mapped with the station. Thechannel access method may insert an additional RAW by logical groupingaccording to a device type and the like in the sector interval. Whensector dedicated RAWs, which are prescheduled in the sector interval andnotified by the sector beacon and the omni beacon, are expired,remaining time of the sector interval may be returned for additionalresources used for transmission and reception of the sector and allsectors.

For example, when data transmission and reception with stations of apredetermined second sector is completed before a sector interval 710with respect to the second sector is all elapsed, the channel accessmethod may return remaining time 720 of the sector interval 710 withrespect to the second sector so that other sectors may use the remainingtime 720.

Such return may also be prescheduled and notified in advance by the omnibeacon. However, when unscheduled necessity of return occurs, thechannel access method may notify the return by sending sync frames toall sectors or to sectors available after the return through omnidirectional transmission. The sync frame may be an NDP type sequencethat includes the AP address such as BSSID and a combination of numbersof the sectors available after the return. The combination of theavailable sector numbers may record sector numbers added to an originalsector. Here, when re-return to the original sector is necessary, thechannel access method may use the sync frame of the same use.

The channel access method may have the NDP sector sweep right after thereturn time with respect to other sectors when having the additional NDPsector sweep in the sector interval.

Hereinafter, various embodiments applicable to the foregoing channelaccess method will be described.

The channel access method may configure an omni beacon in the form ofsweeping of a sectored beam. Through this, the channel access method maysolve a coverage mismatch between the omni beacon and a sector beacon.

Depending on embodiments, according to the channel access method,information on a time slot and a sector for allocation before the beacontransmission may be appointed between the AP and the station.

The channel access method may adjust each sectored time window byreflecting that distribution of stations may be varied according to adirection from the AP.

According to the channel access method, since the AP is aware of arelative angular position of the non-TIM device, the AP may determinewindow distribution. Therefore, according to the channel access method,it may be prevented that the AP may not even listen an entering of thenon-TIM device, which is different from in the logical grouping.

Depending on embodiments, even in the same BSS, the channel accessmethod may be affected or not affected according to sectors due tooverlapped BSS (OBSS). Therefore, a channel which is unavailable due tointerference in a particular sector may be available in other sectors.Thus, the channel access method may be applied differently according tothe sectors.

To achieve MU-MIMO grouping, which is more proper in view of channelorthogonality, by stations belonging to different sectors, the channelaccess method may inevitably set a window capable of simultaneoustransmission of a plurality of sectors.

When the station moves from a sector to another sector, an addresschange in a TIM map may be included so that the AP is aware of thesector to which the station is moved. In addition, the channel accessmethod may use a reassignment protocol, and additionally use a protocolsimilar to a TIM/non-TIM switch, which notifies various changesoccurring in the logical grouping.

FIGS. 8 and 9 are diagrams illustrating a beacon message and an intervalin a WLAN system according to another embodiment of the presentinvention.

Referring to FIG. 8, the channel access method according to theembodiment of the present invention may use only one beacon asconcatenated beam sweeping. In this case, a first sector interval 810, asecond sector interval 820, and a third sector interval 830 may beconcatenated.

Referring to FIG. 9, the channel access method may transmit a sectoredbeacon for each sector at the same time. In this case, a beacon 910 withrespect to a first sector, a beacon 920 with respect to a second sector,and a beacon 930 with respect to a third sector may be simultaneouslytransmitted.

According to the channel access method, a sectorized beamtraining/feedback may be used for the AP to allow learning an optimalsector for the station. Here, the AP may transmit a sectorized beamalong with sector/group IDs. The station may observe which sector isoptimal and feedback the sector/group ID to the AP. Since the optimalsector may be stabilized as to a fixed station, the feedback may benecessary only once or not frequently. The AP may be aware of theoptimal sector of the station. The AP may associate with stations of aparticular group based on the sector of the station.

FIG. 10 is a diagram illustrating sectorized beam operation according toan embodiment of the present invention.

Referring to FIG. 10, the AP may transmit omni beacons having aperiodical sector beam training session 1010. The station may transmit asector/group feedback to the AP, and the AP may associate with thestation through a particular group corresponding to the sector of thestation. The AP may switch the sectorized beam operation during aparticular transmission opportunity (TXOP) with respect to one stationin a RAW with respect to a particular TIM group or in one sector. Duringa RAW using an NDP, for example sounding NDP with Nsts=1, sector beamtraining may be located after a beacon. The AP may have a fixed schedulerelated to the training RAW. A station sector/group feedback format isto be defined.

According to the channel access method, (NDPA+) NDP or new frames of asector sweep may be used to reduce time duration. The sector sweep maybe grouped as an independent RAW to prevent influences between datatransmission and sector sweep by sectorized or omni-directionaltransmission. In addition, the sector sweep grouped as a RAW may come ata predetermined time indicated by a Global Packet Radio Service (GPRS)included in the omni beacon. Here, the sector sweep RAW may include atleast one piece of information selected from a total number of sectors,a current sector number per sector number, duration start time of asector report RAW with respect to each sector per sector frame, an APaddress, a spatial stream number, a bandwidth (BW), and the like.

After the station learns the sector number by receiving the sectorsweep, the station may report a sector number of the station to the APduring a BSS interval following the sector sweep. To avoid interferencefrom general sector data transmission or omni-directional datatransmission, a corresponding sector may have a dedicated RAW for thesector report with respect to the station having learned the sectornumber to match a sectorized coverage between a transmitter TX and areceiver RX. For example, referring to FIG. 11, the station havinglearned the sector number according to a first sector sweep RAW 1110 maytransmit a first sector report RAW 1120 to the AP. In the same manner,the station having learned the sector number according to a second sweepRAW may transmit a second sector report RAW to the AP. Also, the stationhaving learned the sector number according to a third sweep RAW maytransmit a third sector report RAW to the AP.

According to the channel access method, when all beacons are omnibeacons, all beacon intervals may be used as RAWs according todetermination by the AP with respect to the sector or omni. Allscheduling information may be supported by GRPS information in the omnibeacons.

When the beacons include sector beacons and one omni beacon, sectorbeacon intervals may be used basically for data transmission for thesector. An omni beacon interval, that is, the BSS interval, may be usedbasically for omni or multi sector data transmission. Additionally, aremaining duration of the sector beacon intervals may be allowed to bereturned by omni-directional or multi sector data transmission. The GRPSinformation in the omni beacons may include at least one piece ofinformation selected from a duration starting time of sector-dedicatedRAWs during each sector interval, duration which may reiterate in a GRPSof an omni-full beacon, and the like.

Another embodiment of the fast sector discovery process will now bedescribed.

Depending on embodiments, the sectorization type may be plural. Forexample, the sectorization type may be two types including a type 0which is the beacon interval based on the sector and a type 1 which is aRAW or TXOP based on the sector. The beacon type may be plural. Forexample, the beacon type may be two types including the sector beacon(type 0) and the omni beacon (type 0 or type 1). Sector capabilitiesexchange may include sector transmission capable of an AP duringassociation, a sector report capable of the station, and a total numberof sectors. In case of sector operation indication, a period of thesector beacon, a predetermined sector ID/group ID (type 0), and a nextsector training time (type 1) may be in the beacon or a response state.In case of an AID change, a first AID may be acquired based on thesector or an AID may be acquired based on the omni first and thenreallocated.

The sector discovery process may be performed by various embodimentsaccording to the sectorization type.

When the sectorization type is the type 0, that is, the beacon intervalbased on the sector, the channel access method may perform the sectordiscovery process in order of sector beacon (a sector capacity of theAP, a period of the sector beacon, a sector ID)=>sectordiscovery=>association (AID acquisition, a sector capacity of thestation)=>beacon (a group ID). Alternatively, the channel access methodmay perform the sector discovery process in order of the sector beacon(the sector capacity of the AP, the period of the sectorbeacon)=>association (AID acquisition, the sector capacity of thestation)=>sector discovery=>AID reassignment=>beacon (sector ID/groupID). Alternatively, the channel access method may perform the sectordiscovery process in order of the omni beacon (the sector capacity ofthe AP, the period of the sector beacon)=>association (AID acquisition,the sector capacity of the station)=>sector discovery during sector/omnibeacon interval=>AID reassignment=>beacon (sector ID/group ID).Alternatively, the channel access method may perform the sectordiscovery process in order of the omni beacon (the sector capacity ofthe AP, the period of the sector beacon)=>sector discovery during theomni beacon interval=>association (AID acquisition, the sector capacityof the station)=>beacon (sector ID/group ID). Alternatively, the channelaccess method may perform the sector discovery process in order of proberequest and response (the sector capacity of the AP, the sector capacityof the station, the period of the sector beacon)=>association (AIDacquisition)=>sector discovery during the sector or omni beaconinterval=>AID reassignment=>beacon (sector ID/group ID). Alternatively,the channel access method may perform the sector discovery process inorder of probe request and response (the sector capacity of the AP, thesector capacity of the station, the period of the sector beacon)=>sectordiscovery during the omni beacon interval=>AID reassignment=>beacon(sector ID/group ID).

Depending on embodiments, a selection structure according to sectorcapabilities or sector types exchanged during the association may beincluded, as a structure commonly applied to the type 0 and the type 1which are the sectorization types. In addition, the type 1 may notinclude sector ID information in the beacon. However, the type 1 mayspecify the sector ID with respect to a particular RAW.

Depending on embodiments, the channel access method may use a periodicRAW (PRAW), that is, the NDP sweep type, for training. Generally, sincea sector beacon cycle mostly corresponds to a long beacon, the PRAW (NDPsweep type) for training may be needed. Here, the channel access methodmay additionally define a subfield (Check an NDP form in 11 c sounding).

FIG. 12 is a diagram illustrating a sector training operation in asectorization type 0, according to an embodiment of the presentinvention.

Referring to FIG. 12, the station may initialize the sector training bytransmitting +HTC frame 1210 setting an Antenna Selection Command/Data(ASELC) set to 1 according to a sector training request. The AP maycontinuously transmit training NDPs separated by the SIFS in the TXOP.The continuous training NDPs may be TXOP holders without acknowledgement(ACK) with respect to other sectorized beams. Each training NDP may betransmitted with respect to one sector beam. The +HTC frame 1210 settingan announcement subfield to 1 may be located prior to a first trainingNDP frame. The location of the training NDP frame may correspond tosector IDs of the sectorized beams. The stations may perform training byestimating received signal quality corresponding to each training NDP.The stations may participate in the training by receiving sectortraining frames. The stations may response to a selected sector ID usinga TBD sector ID feedback in the following TXOP.

According to the channel access method, in case of the announcement-NDPfor Very High Throughput (VHT), different from type 1 sector discoveryinitialized to discover an optimal sector number by the station, type 0sector discovery may be used by a great number of devices searching fortheir optimal sector IDs. Therefore, sounding signaling of abroadcasting type initialized by the AP may be very efficientlyperformed. To apply such a method to S1G sector sounding, at least oneof a plurality of announcement-NDP frames may be an AID of TA=>AP, anAID of RA=>station, or a broadcasting type among NDPA announcementframes. TA or RA may be inserted in a SIG field of the NDP.

According to the channel access method, out of the NDPs, continuous NDPswith SIFs interposed therebetween are located in each sector beam. Acurrent sector ID may be inserted in the SIG field of the NDP. A totalnumber of the sectors may be inserted in the SIG field of the NDP. Afollowing table shows an NDP 1 MHz mode format for the broadcast sectordiscovery, according to an embodiment of the present invention.

TABLE 3 Field Bit width Comments Message type indicator 4 1 bit: NDPindication 3 bits: sub-type indication RA 0 All broadcast TA 9 PBSSIDCurrent sector number 4 From 0 to total sector number-1 Total sectornumber 4 Up to 16 Time to sector report 4 Time to sector report whencurrent sector is chosen. TBD. Reserved bit 1 Tail bits 6 CRC 4 TOTAL 36

In addition, a table below shows an NDP 2 MHz mode format for thebroadcast sector discovery, according to an embodiment of the presentinvention.

TABLE 4 Field Bit width Comments Message type indicator 4 1 bit: NDPindication 3 bits: sub-type indication RA 9 AID or “All zero” forBroadcast TA 9 PAID Current sector number 4 From 0 to total sectornumber-1 Total sector number 4 Up to 16 Time to sector report 4 Time tosector report when current sector is chosen. TBD. Reserved bit 4 Tailbits 6 CRC 4 TOTAL 48

According to the channel access method, broadcast sector NDPs with theinterposed SIFs may be protected by periodic RAWs which are accessibleonly from the AP, for stable broadcast sector sounding. The sector NDPPRAW may be indicated by RPS I.E. of the beacon. The stations mayperform sector training by estimating received signal qualitycorresponding to each training NDP. The stations may participate in thetraining by receiving the sector training frames. The stations mayresponse to the selected sector ID using the sector ID feedback. Toavoid the hidden node problem from a lot of sector reports, a sectorreport with respect to a particular sector selected as the optimalsector may be protected by the RAW accessible by only the station thatselects the particular sector as the optimal sector. Time with respectto the RAW from the corresponding sector sounding may be expressed inthe SIG field of the corresponding NDP sounding.

Depending on embodiments, the type 0 sector discovery may include sectorfeedback I.E. defined by MAC. The sector feedback I.E. may include afield such as TA, RA (AP for avoiding conflict from OBSS), the selectedsector ID, and the like. A following table shows the sector feedbackI.E. according to an embodiment of the present invention.

TABLE 5 Elements ID Length RA TA Chosen sector ID Reserved 1 1 6 6 1

A following table shows NDP 1 MHz mode format for sector feedbackdefined by PHY, according to an embodiment of the present invention.Depending on embodiments, all the NDP types for sector discovery mayhave only one message type.

TABLE 6 Field Bit width Comments Message type indicator 4 1 bit: NDPindication 3 bits: sub-type indication RA 9 PBSSID TA 9 PAID Currentsector ID 4 Reserved bit 0 Tail bits 6 CRC 4 TOTAL 36

A following table shows NDP 2 MHz mode format for sector feedbackdefined by PHY. All the NDP types for sector discovery may have only onemessage type.

TABLE 7 Field Bit width Comments Message type indicator 4 1 bit: NDPindication 3 bits: sub-type indication RA 9 PBSSID TA 9 PAID Currentsector ID 4 Reserved bit 12 Tail bits 6 CRC 4 TOTAL 48

According to the channel access method, the training NDP may include anNDPA format and an NDP format, that is, the sector ID. A sector reportby STA may include an AID reassignment request frame. An ACK by AP mayinclude AID reassignment.

The operation of the AP according to an embodiment of the presentinvention may notify the beacon sectorized to the type 0 or the type 1,and a sounding RAW time. In the type 0, dedicated sounding RAW may alsobe notified for stations of which sector IDs are undefined. Depending onembodiments, the AP may not perform transmission in beacon RPS butinclude RAW signaling for receiving. The report RAW may be provided toprevent an inter-sector hidden node following a plurality of soundingRAWs and a hidden node by unknown STAs. In addition, slots may beallocated in the report RAW or the RAWs of each sector.

The operation of the station may include exchanging the sectorcapabilities information with the AP during the association. The sectorID may be allocated during the association or a temporal AID may beallocated when the sector ID is unknown yet. The station may be aware ofthe sectorization type through the beacon, that may be present in acurrent beacon interval, aware of the sounding PRAW time, and aware of astarting point of the sector report RAW according to the sounding PRAWtime. The station may perform only receiving but not transmission at allduring the sounding PRAW, thereby recognizing the received sector ID.Also, the station may select a preferred sector ID by measuring SNR withrespect to the received sector ID. The station may wake up at thestarting point of the sector report RAW and may transmit (NDS) PS-POLLtogether with the sector AID. The AP being aware of a reassignmentobject of the sector may transmit the ACK by including an AID to benewly set in the ACK. The station may wake at the starting point of thesector report RAW, transmit the NDP PS-POLL, receive the ACK from theAP, wake at a dedicated RAW starting point, thereby knowing slotinformation of the station, and wake in the corresponding slot. Thechannel access method may transmit the sector report at a starting pointof the slot and may be reassigned with the AID as the ACK.

As an operation for the sectorization, the AP and the station mayexchange the sector capabilities during the association to find a typeof possible sectorized transmission or whether the sectorizedtransmission is possible. Alternatively, the AP and the station maytransmit the beacons. The AP may transmit a beacon including a sectoroperation field (type 0 or type 1).

A following table shows the sector capabilities element in the operationfor the sectorization.

TABLE 8 Subfield Bits Definition Encoding Element ID 8 Length 8Sectorization 1 indicate whether the Set to 0 if not Beam Capable AP orSTA supports supported, Set to the sectorized 1 if supported operationSectorization 2 indicate supports of Set to 0 if only Type 0 Type whichtype of Sectorization is sectorization scheme supported, Set to 1 ifonly Type 1 Sectorization is supported, Set to 2 if both Type 0Sectorization and Type 1 Sectorization are supported, Set to 3, elseTotal Sector 3 Indicate the total Set to 0 to 7 to Number number ofsectors AP represents number of supports in the BSS sector 1 to 8,respectively Sector ID 1 indicate whether the Set to 0 if not FeedbackSTA supports sector supported, Set to Capable ID Feedback 1 if supportedSector Training 1 Indicate whether the Set to 0 if not Capable AP or STAsupports supported, Set to sector training 1 if supported Reserved TBD

The channel access method according to the embodiment may search for thesector ID for the station. In the type 0 sectorization, when the stationis associated during the sectorized beacon interval, the channel accessmethod may transmit the sector ID of the station to the AP. The AP mayset the AID of the AP based on the sector ID. Alternatively, the stationmay not only detect a maximum sector for stable communication but alsowait for other sectorized beacons. During the omni beacon interval, whenthe station is associated, the AP may temporarily set the AID of thestation until the station discovers its optimal sector. Therefore, theAP may be continuously associated with stations which have not foundactual AIDs proper for the optimal sector IDs and have only thetemporary AIDs. For all the stations to quickly match their minimumsectors, fast sector training of on-demand may be necessary. Also, thefast sector training of on-demand may be necessary to reduce a great airtime necessary for an entire cycle of all the sectorized beaconintervals in the type 0 sectorization.

In the fast sector discovery process according to yet anotherembodiment, in case of the type 0 sectorization, the AP may set aperiodical sounding RAW based on a number of sectorable stations inwhich the temporary AIDs are piled up in the AP information. During thesounding RAW with respect to all the AIDs or some limited AIDs, a non-APSTA having a corresponding AID may be prevented from being transmittedto anywhere for stable sounding. However, the non-AP STA need to wake upto hear the whole sounding. One bit indication may be used for theforegoing operation of new stations. The bit may be applied to explicitFAST channel discovery.

A following table shows RAW parameter set elements according to anembodiment.

TABLE 9 Feature Value Interpretation Page ID TBD bits Indicates the pageindex for hierarchical AID (based on hierarchical AID) of the allocatedgroup Block Offset TBD bits Assuming 32 blocks per page, these bitsindicate the starting block index of the allocated group Block Range TBDbits Indicates the number of blocks (starting from the block offset) forthe allocated group RAW   8 bits Duration in TU from end of beacon StartTime transmission to RAW Start time RAW Duration TBD bits Duration ofRAW in TU Access   2 bits Bit 1: Set to 1 if only STA with their TIM bitrestricted set to 1 are allowed to perform UL to paged transmissions Bit2: Set to 1 if RAW is STA only reserved for frames with duration smallerthan slot duration, such as PS-Polls/trigger frames (ignored if Bit 1 isnot set) Group/   1 bit Set to 1 to indicate if STAs need to wake upResource at the beginning of the RAW to receive allocation groupaddressed frames such as resource frame allocation (format of theresource allocation indication frame TBD) Sounding   1 bit Set to 1 toindicate if non-AP STAs are RAW prohibited to transmit but have tolisten the entire RAWSet to 0 otherwise Slot TBD bits Include - Slotduration signaling - Slot definition assignment to STA - Cross boundarytransmissions allowed/not allowed Format is TBD

FIG. 13 is a diagram illustrating a sounding RAW and a sector report RAWaccording to an embodiment of the present invention.

Referring to FIG. 13, the channel access method according to theembodiment may use a +HTC NDPA-NDP field along with modification in asounding RAW 1310. NDPA may be omitted from the sector sounding. NDP CTSmay be used for NDP sweep for sector training. For more stable sectordiscovery, a sector ID for an NDP component may be added to a SIG fieldof the NDP CTS. TBD fits for NAV setting in the stations may be definedto protect currently accessing mediums and the stations. Since only theAP is capable of data transmission during the sounding RAW, the sectorID may share a duration field. A following table shows an NDP componentfield according to an embodiment.

TABLE 10 Message Type Address RA Address/ Duration/ Early SectorIndicator Indicator Partial BSSID Sector ID Indicator Reserved CRC TailBits TBD 1 TBD TBD TBD (1) TBD 4 6

In the channel access method according to the embodiment, the AP mayexchange sector capabilities information with the stations during theassociation. The AP may notify the beacon (type 0 sectorization) ofstarting points of the sounding RAW and the sector report RAWs. The APmay notify a dedicated sounding RAW for the stations of which sector IDsare undefined. The AP may not perform transmission to the beacon RPS butinclude dedicated RAW signaling for receiving. Here, a report RAW may beprovided to prevent an inter-sector hidden node following a plurality ofsounding RAWs and a hidden node by unknown STAs. In addition, the AP mayallocate slots in a report RAW1 or the RAWs of each sector if necessary,and may receive PS-POLL from the stations which are to report the sectorIDs. The AP having received the PS-POLL from the stations may notify acorresponding dedicated report slot time of a sector report RAW2 throughACK with respect to a temporary ID. When reported with a preferredsector ID in each slot of the sector report RAW2, the AP may notify anAID to be newly allocated, as the ACK.

The station may exchange the sector capabilities information with the APduring the association. Depending on embodiments, the sector ID may beallocated during the association, or a temporary AID may be allocatedsince the sector ID is unknown yet. The station may be aware of thesectorization type through the beacon, aware of the sounding PRAW time,which may be present in a current beacon interval, and aware of astarting point of the sector report RAW according to the sounding PRAWtime. The station may perform only receiving but not transmission at allduring the sounding PRAW, thereby recognizing the received sector ID.Also, the station may select a preferred sector ID by measuring SNR withrespect to the received sector ID. The station may wake up at thestarting point of the sector report RAW1 and may transmit (NDS) PS-POLLby the current temporary AID. Therefore, the AP becomes aware ofreassignment objects of the sector and may receive information on acorresponding report slot of the sector report RAW2 in the ACK. Thestation may wake up at the corresponding report slot of the sectorreport RAW2, transmit the NDP sector report, and accordingly beconfirmed with respect to the sector discovery by receiving the ACKincluding the AID allocation information from the AP.

A following table shows fields of the sector report frame (1 MHz) in thechannel access method according to the embodiment. Here, the sectorreport may be transmitted from the station during the sector reportRAW2.

TABLE 11 Field Bit width Comments Message type indicator 4 1 bit: NDPindication 3 bits: sub-type indication RA 9 PBSSID TA 9 PAID Preferredsector ID 3 Reserved bit 1 Tail bits 6 CRC 4 TOTAL 36

A following table shows fields of the sector report frame (2 MHz) in thechannel access method according to the embodiment. Here, the sectorreport may be transmitted from the station during the sector reportRAW2.

TABLE 12 Field Bit width Comments Message type indicator 4 1 bit: NDPindication 3 bits: sub-type indication RA 9 PBSSID TA 9 PAID Preferredsector ID 3 Reserved bit 13 SNR (5bits) + Received Sector Bitmap (5bits)may be considered Tail bits 6 CRC 4 TOTAL 48

In the channel access method according to the embodiment, a sectorconfirm frame may be transmitted from the AP during the sector reportRAW2. Here, the sector confirm frame may include an AID response elementformat as shown in a table below.

TABLE 13 AID Switch Wakeup Element ID Length AID Count Interval Octets:1 1 2 1 2

As described above, when there is remaining time in the sector interval,the channel access method may reuse the remaining time for othersectors.

It is hard that the sectorized beacon intervals have the same number ofcorresponding sectorized stations. Therefore, the sectorized beaconintervals need to be allowed for reuse for omni directional transmissionof the AP. After transmission of the sector data during the beaconinterval is completed, other sectors may also be reused. When the sectordata transmission during the beacon interval is completed, other sectorsor omni sectors may be allowed to be reused for a remaining intervaluntil the next beacon.

The sync frame may be transmitted to all the sectors to inform that theremaining duration of the sectorized beacon interval may be reused inother sectors when necessary. A following table shows SIG fields of theNDP CTS, that is, the sync frame as a switch for all the sectors,according to an embodiment.

TABLE 14 Message Type Address RA Address/ Early Sector Switch toIndicator Indicator Partial BSSID Duration Indicator All sector ReservedCRC Tail Bits TBD 1 TBD TBD TBD(1) 1 TBD 4 6

The channel access method may discover the sector ID for the station. Incase of the type 1 sectorization, since the beacons are the omnibeacons, all the stations may be associated without sector information.In addition, the sector training using +HTC NDPA-NDPs may be acceptedaccording to the on-demand of the sector.

The above described channel access method may be directly performed by achannel access apparatus. The channel access apparatus according to anembodiment of the present invention may be a module inserted in an AP.

The channel accessing apparatus may include a beacon transmission unitand a data transmission and reception unit.

The beacon transmission unit may transmit a sector beacon with respectto any one sector of a plurality of sectors. In addition, the datatransmission and reception unit may transmit and receive data withrespect to at least one station in any one sector during a predeterminedsector interval. Additionally, the beacon transmission unit and the datatransmission and reception unit may perform sector beacon transmissionand data transmission and reception in sequence, with respect toremaining sectors of the plurality of sectors.

The beacon transmission unit may transmit an omni beacon with respect toall of the plurality of sectors. The data transmission and receptionunit may transmit and receive data with respect to at least one stationof the plurality of sectors during a predetermined BSS interval.

Depending on embodiments, the channel access apparatus may furtherinclude a sector discovery unit. The sector discovery unit may proceedwith the sector discovery process by performing sector sweep.

Since the channel access method described with reference to FIGS. 1through 13 may be directly applied to the channel access apparatus, adetailed description will not be repeated.

The above-described embodiments may be recorded, stored, or fixed in oneor more non-transitory computer-readable media that includes programinstructions to be implemented by a computer to cause a processor toexecute or perform the program instructions. The media may also include,alone or in combination with the program instructions, data files, datastructures, and the like. The program instructions recorded on the mediamay be those specially designed and constructed, or they may be of thekind well-known and available to those having skill in the computersoftware arts. Examples of non-transitory computer-readable mediainclude magnetic media such as hard disks, floppy disks, and magnetictape; optical media such as CD ROM disks and DVDs; magneto-optical mediasuch as optical discs; and hardware devices that are speciallyconfigured to store and perform program instructions, such as read-onlymemory (ROM), random access memory (RAM), flash memory, and the like.Examples of program instructions include both machine code, such asproduced by a compiler, and files containing higher level code that maybe executed by the computer using an interpreter. The described hardwaredevices may be configured to act as one or more software modules inorder to perform the operations and methods described above, or viceversa.

A number of examples have been described above. Nevertheless, it will beunderstood that various modifications may be made. For example, suitableresults may be achieved if the described techniques are performed in adifferent order and/or if components in a described system,architecture, device, or circuit are combined in a different mannerand/or replaced or supplemented by other components or theirequivalents.

Accordingly, other implementations are within the scope of the followingclaims.

1. A channel access method by an access point (AP) having a sectorantenna in a wireless local access network (WLAN), the channel accessmethod comprising: transmitting a sector beacon with respect to any onesector among a plurality of sectors; transmitting and receiving datawith at least one station in any one sector during a pre-scheduledsector interval; sequentially performing transmission of the sectorbeacon and transmission and reception of the data with respect toremaining sectors of the plurality of sectors excluding the any onesector; transmitting an omni beacon with respect to all of the pluralityof sectors; and transmitting and receiving data with respect to at leastone station of the plurality of sectors during a pre-scheduled BasicService Set (BSS) interval.
 2. The channel access method of claim 1,wherein a reception mode of the sector antenna is an omni-directionalmode.
 3. The channel access method of claim 1, further comprising:performing a sector discovery process by performing sector sweep.
 4. Thechannel access method of claim 3, wherein the performing of the sectordiscovery process comprises: defining the sector sweep as a no dataprotocol (NDP) type signal sequence.
 5. The channel access method ofclaim 3, wherein the performing of the sector discovery processcomprises: designating the sector sweep as a restricted access window(RAW).
 6. The channel access method of claim 3, wherein the performingof the sector discovery process comprises: performing the sector sweepin the BSS interval.
 7. The channel access method of claim 6, whereinthe omni beacon includes location of the sector sweep in thepre-scheduled BSS interval.
 8. The channel access method of claim 3,further comprising: being reported with a discovery result from astation that discovered an optimal sector the station belongs to throughthe sector discovery process.
 9. The channel access method of claim 1,further comprising: receiving a sector discovery request from a stationto perform fast sector discovery; performing additional sector sweep inaddition to the pre-scheduled sector sweep; and receiving a result ofthe fast sector discovery from the station.